Support viewfs in Sentry Namenode plugin

The View File System (ViewFs) provides a way to manage multiple Hadoop file system namespaces (or namespace volumes). It is particularly useful for clusters having multiple namenodes, and hence multiple namespaces, in HDFS Federation. ViewFs is analogous to client side mount tables in some Unix/Linux systems.

In a ViewFs deployment, Sentry MetastorePlugin sees viewfs schemed paths but drops them in PathsUpdate.parsePath as it hardcodes the support for only hdfs schemed path.

If paths updates are sent to Sentry Namenode plugin, the viewfs paths need to be converted to per-namenode (HDFS cluster) paths.